1. Field of the Invention
The present invention relates to record medium assemblies useful in high density storage of information by optical writing and/or reading, and more particularly to improved configurations for optical disk assembly retaining rings.
2. Description of the Prior Art
The currently preferred optical disk technology employs disk elements with spiral or concentric tracks of minute (e.g., on the order of a micron or less in size), optically-detectable marks. One real-time mode of recording (writing) such marks is by scanning tracks on the disk with an equivalently small beam of radiation (e.g., from a laser) which is modulated "off or on" according to an electrical signal representative of the information to be written. Information is recovered (read) by scanning the tracks with the same size or only slightly larger, but still very tightly focused, radiation (e.g. light) spot. The recovered information is in the form of a fluctuating electrical signal obtained from a photodetector that senses the read-out light reflected from the recorded disk.
In order to write and read information in the form of such minute markings, optical systems of high numerical aperture are used to focus light to equivalently minute spots. Such optical systems have extremely small depths of focus and the proper positional relation between the writing or reading optical system, and the optical disk record surface must be stringently maintained both smooth and flat.
One approach to achieve requisite smoothness, flatness and protective requirements for high density storage of information is disclosed in commonly-assigned, copending U.S. patent application Ser. No. 264,313, filed May 18, 1981 in the names of F. F. Geyer and E. M. Leonard. In that approach an improved optical disk assembly adapted for high density storage of information comprises (i) a flexible, disk-shaped support carrying a record layer; (ii) a transparent disk-shaped cover sheet opposing the record layer, and (iii) an annular retaining ring for holding the support and cover sheet in tension.
Attachment of the support and cover sheet to the retaining ring should be done such that the tension in the support and cover sheet is substantially circumferentially-symmetric, and such that the tension is held after attachment. The present invention provides for such attachment of the support and cover sheet to the retaining ring and further provides a surface for accurately centering the disk assembly on rotatable receiving structure of optical disk write/read apparatus such that information tracks on the record layer are closely concentric with the axis of rotation of the receiving structure. The greater the amount of eccentricity of the mounted disk assembly, the more difficult it is for the write/read optics to follow the information tracks.